Most, but not all patients with hypertrophic cardiomyopathy, report symptom benefit following operative relief of left ventricular outflow obstruction. In order to determine predictors of exercise benefit, 25 patients underwent preoperative and 6 month post-operative catheterization and exercise hemodynamic measurements. Increase in oxygen consumption between preoperative and postoperative treadmill exercise tests (Bruce protocol) was chosen as an index of exercise benefits. Twenty-two different variables were investigated for predictive significance. Univariate analyses indicated preoperative left ventricular end-diastolic pressure and post-operative reduction in left ventricular end-diastolic pressure as significant predictors of post-operative increase in maximum oxygen consumption during exercise. There was borderline significance for post-operative reduction in left ventricular outflow gradient. Multivariate step-wise regression analysis of preoperative hemodynamic variables selected preoperative left ventricular end-diastolic pressure as a significant predictor of post-operative increase in oxygen consumption during exercise. We conclude that elevated left ventricular filling pressures identify patients most likely to demonstrate exercise benefit following relief of outflow obstruction in hypertrophic cardiomyopathy.